The clinical utilization of a pointed hollow needle mounted inside a flexible catheter tube is well known in the medical art for the introduction of a catheter. In such a medical instrument, the catheter tube is positioned tightly around the needle in such a way as to allow the needle to slide and telescope along the length of the catheter tube. Before use, the tip of the needle is protruding slightly through the opening of the catheter tube to allow facile penetration through the skin. Upon puncturing of the skin and introduction of the needle, the distal end of the catheter tube is simultaneously brought into place inside the desired target body cavity of the patient, such as the inside of a blood vessel, for example a vein. The needle has then done its duty in assisting the introduction of the catheter and is withdrawn by being pulled backwards through the catheter. Upon release of the needle, the catheter is set in its intended working mode extending over a lengthier period of time and including, for example, periodical administration or infusion of fluids or medications in liquid form, the collection of blood samples and the like.
An unprotected released needle constitutes, however, a serious health hazard due to the fact that it may be contaminated with e.g. infectious agents originating from the patient's blood or other body fluids, in combination with the needle tip's inherent ability to easily penetrate skin. Hence, the medical personnel who are handling the released needle may acquire the corresponding disease, e.g. HIV or hepatitis, if by accident contacting it with their skin. In order to circumvent or alleviate the health hazards associated with such a released needle amongst other things, there has been much effort devoted to the development of various kinds of needle tip protectors with a special focus on automatic variants of a type which may be referred to as being “foolproof”.
Factors of relevance for the design of automatic needle tip protectors include the choice of material and the protector's interaction with immediate contacting parts of the medical instrument.
With regard to the choice of material, protectors may be divided into two main categories, metallic or polymeric. Advantages of polymeric or plastic needle tip protectors, in comparison to metallic ones, include reduced noise or scraping vibrations as the needle is withdrawn from the catheter. In addition, they may be produced by e.g. molding, which offers greater design opportunities.
If the protector is mounted so that it is contacting a part of the medical device which may communicate with e.g. a vein of a patient, it is desirable to avoid the inclusion of sharp edges and the like in the design of the protector. Such edges or similar shapes may result in scrapings and release of particles or flakes which represents a health hazard to the patient. Thus, it is desirable to design the protector such that only smooth shapes of it is contacting critical parts of the medical device, such as the inside of a catheter hub.
Contacting smooth shapes of two bodies, such as the protector and a part of the medical instrument may, however, result in a significant attraction between these parts, especially if the contact area is large and they are pressed together. The underlying basis for this type of attraction include intermolecular attraction between the molecules of the two bodies, in which molecular van der Waals interactions and surface tension of the two bodies are important factors. Covalent bond formation between closely interacting surfaces may also contribute to the attraction. This type of attraction may become noticeable when the protector, or a part thereof, is about to be released from the contacting part of the medical device as a part of its intended function. The force needed to release the protector, or a part thereof, from the device then becomes significantly higher than expected. This effect, which will be referred to as “the attraction effect” from here on, may even adventure the intended function of the protector if relying on e.g. an automatic release of a part of the protector, such as a spring biased arm or the like, from a part of the medical device, such as the interior of the catheter hub.
GB2451153A by Poly Medicure Ltd discloses a needle safety device for an intravenous catheter apparatus that includes a base, which may be made of a plastic material, capable of receiving a needle between opposing jaws attached to the base and capable of being influenced by the needle. The jaws have a link connecting the jaws arranged a distance from the base. The jaws may move between an expanded position in which they interact with an obstruction within a wing housing of the intravenous catheter apparatus. The jaws permit relative movement of the needle with the base when expanded, close around a needle tip as it passes the jaws, and prevent relative movement of the needle with the base when the jaws are collapsed.
U.S. Pat. No. 5,135,504A by Donald J. McLees describes a needle tip guard that may be made of a plastic material. The presence of the needle keeps the end of the guard flared out and thereby retained inside the catheter hub by e.g. a retaining ring held tightly therein until the needle is withdrawn from the catheter. At that time a slightly widened portion of the needle tip catches the guard, forcing the end of the guard to close over the tip and pulling the guard from the hub.
The function of the needle tip guards described in GB2451153A and U.S. Pat. No. 5,135,504A relies on the presence of one or several obstructions, e.g. protuberances or grooves, of the inside of the catheter hub for keeping the guards at place there until the needle is withdrawn from the hub. Disadvantages of the need of such obstructions include the need to use specially designed catheter hubs which are more expensive and difficult to produce in comparison to simpler standard catheter hubs. In addition, nowhere in GB2451153A or U.S. Pat. No. 5,135,504A is the attraction effect, or a corresponding phenomenon, mentioned. It can therefore not be ruled out that one or several of the guards described therein has been designed without taking this effect into account and, hence, that the function and/or safety of the corresponding guard may be compromised due to this.
Hence, an improved device for automatic shielding of the needle tip of a needle after its employment for introduction of a catheter tube is desired.